Predominance of Char Sorption over Substrate Concentration and Soil pH in Influencing Biodegradation of Benzonitrile

Abstract

Incomplete combustion of field crop residues results in the production of char, a material rich in charcoal-type substances. Consequently, char is an effective adsorbent of organic compounds and when incorporated into soil may adsorb soil-applied pesticides, thereby altering their susceptibility to biodegradation. We investigated the relative importance of char, soil pH and initial substrate concentration in biodegradation of pesticides in soils by measuring the biodegradation of benzonitrile in soil as a function of soil char content (0% and 1% by weight), initial benzonitrile concentration (0.1, 1.06, and 10.2 mg l(-1)) and soil pH (5.2, 6.9 and 8.5). Preliminary experiments revealed that wheat straw char had a much greater benzonitrile sorption capacity than did soil to which the char was added. The extent of benzonitrile degradation decreased as initial benzonitrile concentration increased in both buffer solution and soil slurry. In contrast, the degradation increased as initial benzonitrile concentration increased in char-amended slurry. In un-amended soil slurry, the benzonitrile degradation was lower at pH 5.2 than at pH 6.9 or 8.5, but in char-amended soil slurry the degradation was not affected by pH, again presumably due to adsorption of benzonitrile by the char. Adsorption by soil char appears to be more important than either initial substrate concentration or soil pH in controlling benzonitrile degradation in char-amended soil slurry. The presence of crop residue-derived chars may alter pesticide degradation patterns normally observed in soils and thus significantly affect their environmental fate.

Removal of Pharmaceuticals and Personal Care Products during Water Recycling: Microbial Community Structure and Effects of Substrate Concentration

“…Similar results were found in a continuous-flow system, in which the fraction of applied PPCP biodegraded decreased dramatically when the starting concentration was changed from 0.1 g liter Ϫ1 to 100 g liter Ϫ1 (33). Initial substrate concentrations have been shown to influence the fraction of compound biodegraded for non-PPCP compounds as well, such as pesticide isopropyl N-phenylcarbamate (34), pesticide benzonitrile (35), and herbicide intermediate and biocide 2,4,5-trichlorophenol (36).…”

Residues of bioenergy production chains as soil amendments: Immediate and temporal phytotoxicity

“…Biochar has been found to strongly adsorb herbicides and phytotoxic metals from the soil [32][33][34]. Similarly, a more developed body of research on crop residue char indicates that char is able to strongly adsorb herbicides and reduce their bioavailability better than other forms of organic matter [53,54].…”

Impacts of Biochar (Black Carbon) Additions on the Sorption and Efficacy of Herbicides

“…The authors reported a 2.5-20 fold increase in the K f values following the char addition. Zhang et al (2006) studied the sorption of the pesticide benzonitrile in soil, wheat char and soil amended with the char at a rate of 1% (w/w) with the results of 40.5, >99, and 96.5% respectively, sorbed of the total of the pesticide initially applied. The wheat char was the dominant sorbent phase in the soil amended system, attributing approximately 90% of benzonitrile sorption to the wheat char and 10% to the soil.…”